Honors Theses Geology - Environmental Studies Spring 2015 Assessing ungulates role in riparian hummocking on three national forests in southern Utah Collin W. Smith Penrose Library, Whitman College Permanent URL: http://hdl.handle.net/10349/20151109 This thesis has been deposited to Arminda @ Whitman College by the author(s) as part of their degree program. All rights are retained by the author(s) and they are responsible for the content.
Assessing Ungulates Role in Riparian Hummocking on Three National Forests in Southern Utah By Collin W. Smith A thesis submitted in partial fulfillment of the requirements for graduation with Honors in Geology-Environmental Studies Whitman College 2015
Certificate of Approval This is to certify that the accompanying thesis by Collin W. Smith has been accepted in partial fulfillment of the requirements for graduation with Honors in [major]. Robert Carson Whitman College May 13, 2015 ii
Table of Contents Certification... ii Abstract... iv List of Figures... v Introduction... 1 Nomenclature... 4 Data collection... 5 Support for Ungulate Exacerbation of Hummocking... 7 Support for a Non-livestock Related Hummock Formation Process... 9 Characterization of Study Area... 10 Results... 11 Discussion... 16 Conclusion... 24 Acknowledgments... 26 References Cited... 27 Appendix I: Standard Operating Procedure... 29 Appendix II: Aggregated Site Data... 34 iii
Abstract Very little research has been conducted on the role of ungulates in the development of hummocked topography in wetlands. This survey evaluates 22 hummocked wet meadows and riparian areas on the Dixie, Fishlake and Manti-La Sal National Forests in southern Utah. I explored the variability in location and morphology of hummocked areas in order to better understand the mechanisms of formation at play. The study explores evidence for and against ungulate grazing as factor in hummock formation and/or exacerbation in order to better direct federal land managers approach to wetland protection and mitigation. Hummock oblateness may be an important indicator of ungulate interaction with hummocked wetlands. However, the lack of suitable ungrazed reference areas compounds the difficulty of determining ungulate impact. Two locations with exclosures or lighter grazing regimes present different hummock morphology. iv
List of Figures Figure 1: Hummocks on Fishlake National Forest... 1 Figure 2: Transect diagram... 6 Figure 3: Hummock length vs width for all sites... 11 Figure 4: Hummock sites by slope... 12 Figure 5: Hummock oblateness vs slope... 12 Figure 6: Elevation vs site characteristics... 13 Figure 7a-d: Site comparison, Beef Meadows... 14 Figure 8a-d: Site comparison, Garkane Power Plant/King s Pasture... 15 Figure 9: Hummocks at Ute Cabin Spring... 16 Figure 10: Hummocks at Round Mountain... 17 Figure 11: Serpentine hummock at Webb Hollow... 19 Figure 12: Fenceline, Garkane Power Plant/King s Pasture... 20 Figure 13: Large hummocks at Stink Flat... 22 Figure 14: Exposed rocks at Stink Flat... 23 Figure 15: Summary table of Garkane Power Plant/King s Pasture data... 24 Figure 16: Diagram of hummock plot... 32 v
Introduction Hummocks are small-scale geomorphic features occurring in wetlands throughout the world. A hummock is defined by Washburn (1956) as a particular type of nonsorted net with a mesh characterized by a three-dimensional knoblike shape and cover of vegetation. Hummocks come in a wide variety of sizes, from just 10 cm in height to almost a meter. Diameters range from 10 cm up to over 2 meters. Hummocks are found throughout the Figure 1: Hummocks on the Fishlake National Forest. world, typically at high latitudes and elevations. A variety of hypotheses have been put forward regarding the genesis of these features, including both biotic and abiotic factors. Abiotic hypotheses include differential frost heave, cryoexpulsion of clasts, hydrostatic or cryostatic pressure and cellular circulation due to ice lensing (Grab 2005). Biotic hypotheses that have been studied include accumulation of plant litter, bird perches and ant activity as well as overgrazing by large ungulate animals (Smith et al. 2012). Reviews often come to the conclusion that hummocks are of polygenetic origin or that different categories of hummocks exist and these are caused by unique processes.
While no consensus exists in the scientific literature on the origin of hummocks, range managers in the western United States regularly attribute hummocking in wetlands and riparian areas to livestock activity (Janovsky-Jones 1999; Weixelman and Cooper 2009). However, only a few studies have attempted to directly tease out the connection between ungulate (particularly cattle) grazing and hummock formation, and these have come to conflicting conclusions about whether overgrazing can be linked to hummocking in a statistically rigorous way. In all cases, the lack of large ungrazed areas to serve as a reference point creates difficulty in attributing hummocking to grazing (Smith et al. 2012). To date, no studies or surveys have been published regarding hummocking in Utah. This study examines 20 hummocked sites on the three national forests in southern Utah, the Dixie, Fishlake and Manti-La Sal, as well as on two private inholdings near Boulder, Utah. Surveys were conducted at sites to explore the variability in location, morphology and vegetation communities in the hummocked areas in order to better understand the formation mechanisms at play. Hummocks, if not caused by natural processes, should be of concern to range managers and wetland ecologists in the West. Chimber and Cooper (2003) note that in fens of the southern Rockies, ditching (channelizing) can alter water table depths, vegetation composition, and primary production, and can change peatlands from net sinks to net sources of CO2. Those who point to livestock as a cause of hummocking usually describe some type of trailing at play. For instance, Weixelman and Cooper (2009) found that the shearing caused by the large weight of ungulates results in exposure of the peat layer in fens. Animals walking through fens may 2
expose soil and peat to oxidation. I found some hummocked areas to have significant bare ground and desiccation, even early in the summer. Booth et al. (2014) comment that in the face of declining snow pack and water storage due to climate change, land management practices that affect water retention gain a heightened importance. In particular, they claim that several goals are directly affected by hummocking including maintaining vegetative cover protecting against soil erosion, maintaining or significantly increasing soil organic matter through annual additions of senescing vegetation, and maintaining microtopographic water storage by avoiding channeling that can accelerate runoff. Hummocks may also increase utilization because the vegetation on top of the hummocks is easier to reach than the vegetation in the interspace allowing a higher level of grazing utilization to be reached earlier in the season. Wetlands play an outsize role in the ecology of the West and are rich in plant, animal and aquatic life. At the same time, several factors make wetlands and riparian areas attractive to heavy use by ungulates, including easily accessible water, favorable terrain, hiding cover, shade and an abundance of palatable plants (Kovalchik and Elmore 1991). Overgrazing has already compromised many wetland systems by bank deterioration, trampling and removal of vegetation. These impacts are well-documented and linked to poor grazing management practices. In fact, these impacts are often found in areas with significant hummocking. However, sites also exist where hummocking occurs without other obvious impacts. It is in these locations that clarification on the natural-ness of hummocks is most valuable for setting adaptive management policy. 3
Nomenclature A variety of names are used to describe hummocking processes and end products. The lack of standardization may have led to misunderstandings between the scientific and range management communities. Here, I attempt to provide some clarification to aid communication. Grab (2005) provides a review of several cryogenic mechanisms leading to hummock development. Grab notes that in North America, the term earth hummock is usually associated with intense frost heave in permafrost environments. Conversely, the term thúfur is used to describe features formed by the local displacement of surface material due to seasonal frost penetration. Since there are few permafrost environments in the West, if the features surveyed in this study were indeed caused by frost penetration, they would more accurately be called thúfur. However, no range managers or conservationists I spoke with over the course of the study ever used this term, so I will not use it here. The word hummock has different connotations to different disciplines. Many ecologists think of hummocks as depositional features created through the buildup of organic material like sphagnum moss or the entrapment of eolian or fluvial sediment by vegetation (personal communication, Robert Beschta 2014). On the other hand, geomorphologists will often associate the term hummock with a cryogenic, push-up, process. Range managers, on the other hand, tacitly accept that hummocks are a form of wetland degradation caused in whole or in party by livestock overgrazing. All of these groups are correct on some level, but the 4
presuppositions and lack of distinguishing nomenclature make communication problematic. Another word that might be applied to the features in question is pedestal. Soil pedestals are erosive features often found in upland areas with significant soil erosion due to sheet flow. They form because some binding agent (a shrub, clump of grass, stone, etc.) shields a piece of the soil from the erosion occurring around it. The value of applying the term pedestal to the features studied is that it carries with it an erosive rather than depositional connotation. If the features are in part caused by erosion along cattle trails as some literature claims, then pedestal might be a more appropriate term. Evidence for erosion occurring in hummocked areas will be explored later. In general, this paper will use the term hummock in this paper to describe a knob-like protrusion from the ground, at least 10 cm tall with relief on all sides. The term interspace will refer to the area between two or more hummocks. Data Collection Methods for the study were modified from Smith et al. (2012). At each site surveyed, several characteristic measurements of the hummocked area were taken: location (by GPS), slope, aspect, width and length. Scat observations were also made, recording the prevalence of cow, elk and deer droppings. Sites could be no less than 15 m by 15 m to be included in the study. The perimeter of the site was determined either by the end of the hummocks greater than 10 cm tall, edge of water, or by a headcut (if present). On Forest Service land, allotment and pasture were noted to 5
provide grazing history for the site. A hundred-point transect was set up at each site. The transect was divided into three sections parallel to the long axis of the site and distributed randomly along the long axis of the site. Where each transect reached the perimeter of the site, an edge characterization was made: Gradational - Hummocks become smaller until they are less than 10 cm tall Distinct Hummocks end with heights in excess of 10 cm Headcut A sharp, vegetated break in slope bounds the field of hummocks Stream bound Running water bounds the hummock field Figure 2: Diagram of transect locations at a hummock site. At each point along the transect, cover was recorded by the top vegetation in contact with a 3 long point pin. Cover was recorded as grass, grass-like (e.g. Juncus or Carex spp), forb, shrub, tree, or litter (dead vegetation). Grass and grass-like plants were identified as either rhizomatous or caespitose if possible. Ground cover 6
was also recorded as bare, litter, vegetation, water or rock. Hummock or nonhummock was recorded at each point. The edge of the hummock was defined by where the ground rose above the level of the interspace. To determine hummock density, 2 meter by 2 meter plots were placed at four randomly selected points along the total length of the transect. Within each plot, all hummocks were counted. Flags were placed on the hummocks and a photo was taken. All hummocks that lay more than 50% within the plot were counted. Two hummocks (if present) were randomly selected for height, width and length measurements within each plot. A few sites (Beef Meadows, Stink Flat and Danish Meadows) were too large for the regular sampling procedure. At these sites an alternative method was used. From a point near the center of the site, a random direction and distance were used to find the transect start. From the start, a random direction was chosen for each of three 100-yard transects. The large sites also contained 100 surveyed points. Support for Ungulate Exacerbation of Hummocking Hummocks are frequently noted as in indicator of overgrazing in range management literature (Corning 2002; Janovsky-Jones 1999; Magnusson 1998). The observation is typically stated as fact, although a study is rarely, if ever, cited. Streeter and Andrew (2013) write that earth hummock formation in Iceland s rofabard soil systems is an interplay between frost-action and grazing regime. The strongest evidence for a grazing mechanism for hummock development comes from Booth et al. (2014) who surveyed exclosures on Bureau of Land Management rangeland in the heavily hummocked Sweetwater River system in Wyoming. The 7
authors used an erosion bridge (also called a pin meter) and aerial photography to measure surface roughness both inside and outside several exclosures. Their study showed that surface roughness was on average 50% higher outside the exclosures than inside by the photo analysis and 75% higher by the erosion bridge analysis. Booth et al. (2014) state that their study is not proof that grazing causes hummocks; rather, it is very strong evidence that grazing significantly increases surface roughness roughness that may result from hummock formation and/or deepening inter-hummock channels, and perhaps from other factors. I was unable to find any study claiming that livestock were the sole cause of any hummocking observed at any site. Anecdotally, some scientists interviewed mentioned several indicators that ungulates (including both cattle and other ungulates like elk and deer) exacerbated hummocking. These include the preponderance of bare ground in the interspace between hummocks, hoof shearing on the edges of hummocks, lack of diverse plant composition in hummocked areas, and shorter height and rounding of hummock edges in areas spared from grazing for significant periods (personal communication, Paul Meiman and David Weixelman). Dave Weixelman, range ecologist for the US Forest Service, noted several differences in hummocks he observed during comparative studies of Yosemite National Park and the adjoining Inyo National Forest. Yosemite, which has been ungrazed for over a hundred years, has hummocks generally lower in height and without sign of hoof shearing around hummock sides (personal communication, Dave Weixelman). Lisa Bryant, director of the Bureau of Land Management s Moab District, recalled observing hummocked springs in 8
Colorado highly degraded by elk wallows in areas closed to cattle grazing (personal communication, Lisa Bryant). Support for a Non-livestock Related Hummock Formation Process There is wide consensus in the literature that hummocks can form through processes unrelated to livestock impact. Of these, the most commonly stated is freeze-thaw. In the West this is due to seasonal frost penetration, not permafrost cycling. Smith et al. (2012) performed a wide survey of hummocked and nonhummocked wetlands throughout Colorado. Their study is one of the few to incorporate measures of grazing intensity as well as climate and plant cover. Smith et al. (2012) found that mean winter precipitation, mean annual temperature and forb cover were negatively related to odds of hummock occurrence whereas soil silt content and plant species richness were positively related to odds of hummock occurrence. Lower mean annual temperature supports a freeze-thaw hypothesis of formation because those sites likely experienced freeze-thaw cycles earlier in the fall and later into the spring. Smith et al. (2012) also found increasing odds of hummock occurrence with silt content consistent with a frost heave mechanism of formation. With respect to grazing pressure s influence, a major shortfall in their study is the lack of sites with no history of domestic livestock use. Of 40 hummocked and 40 non-hummocked sites surveyed, only 9 (3 hummocked, 6 non-hummocked) had no recorded use by livestock. Even then, use by wild ungulates like deer and elk was difficult to quantify. Proposed biogenic mechanisms of hummock formation include ant activity (Lessica and Kannowski 1998), bird perches (Verbeek and Boasson 1984), and 9
accumulation of plant litter (tussocks) by wetland graminoids (Dawkins 1939). In the case of the ant and bird perch studies, hummocks were typically isolated, which is not true for the hummock sites captured in this study. Characterization of Study Area All study sites are located on the Colorado Plateau, an extensive region of relatively flat-lying sedimentary strata punctuated by igneous, mountain-forming laccoliths (e.g. the La Sal, Abajo and Henry ranges) and Tertiary volcanic piles more than a thousand meters thick (the High Plateau region). Below about 7,000 (2,130 m) elevation, the area receives very little rainfall and is a desert landscape, deeply dissected into canyons, cuestas and plateaus. In the mountainous regions, elevations reach over 11,000 (3,350 m). The higher elevation regions receive higher rainfall and experience significantly cooler temperatures than the surrounding desert. During the summer, the region receives most of its moisture as intense local, convective storms. Low elevations in the region receive as little as 5 (130 mm) per year while higher regions can receive as much as 26 (660 mm) per year (Schwinning et al. 2008). The lowest elevation site was 7,624 (2,324 m) and the highest was 11,111 (3,387 m). All were located above desert elevation on mountain slopes and high plateaus. 10
Results See Appendix 1 for all site data. 120 Hummock length vs width for all sites 100 Centimeters 80 60 40 20 0 Avg Length Avg Width Figure 3: Distribution of average hummock length and average hummock height for all sites. Average length exceeds average width because hummocks tend to be oblong rather than circular. 11
Hummock Sites by Slope 14 12 10 Number of sites 8 6 4 2 0 0-5% 6-10% 11-15% 16-20% Slope Figure 4: Most hummock sites have a gentle slope. 2 Oblateness vs Slope 1.8 R² = 0.0498 1.6 1.4 Oblateness 1.2 1 0% 5% 10% 15% 20% Figure 5: Slope has no demonstrable impact on the hummock oblateness at the sites surveyed. 12
Figure 6: Climate data on a site level basis was not captured in this study. Elevation is a rough proxy for temperature and precipitation as both generally increase with increasing elevation. No significant relationships were found between hummock characteristics and elevation for the sites surveyed. Length/width 2 1.8 1.6 1.4 1.2 Oblateness y = -5E-05x + 1.9565 R² = 0.0622 1 7000 9000 11000 13000 Elevation (ft) Hummocks/hectare Hummock density 35000 30000 25000 20000 15000 10000 5000 0 y = -0.9434x + 16908 R² = 0.0357 7000 9000 11000 13000 Elevation (ft) % Hummock Cover 60% 50% 40% 30% 20% 10% Hummock Cover y = 1E-05x + 0.1122 R² = 0.0121 0% 7000 8000 9000 10000 11000 12000 Elevation (ft) Length (cm) 120 100 80 60 40 20 Mean length y = 0.0012x + 44.337 R² = 0.0069 0 7000 9000 11000 13000 Elevation (ft) Height (cm) 30.00 25.00 20.00 15.00 10.00 Mean height y = -0.0013x + 29.19 R² = 0.1662 5.00 7000 9000 11000 13000 Elevation (ft) 13
7a) Length vs Width 60 Length (cm) 50 40 30 20 10 Beef meadows Beef exclosure 0 0 20 40 60 Width (cm) 7b) Hummock Density 7c) Oblateness 12000 1.80 Hummocks/hectare 10000 8000 6000 4000 2000 0 7475 10465 Beef Exclosure Beef Meadows Length/Width 1.60 1.40 1.20 1.00 1.36 Beef Exclosure 1.67 Beef Meadows 7d) Height (cm) Hummock Height 30.00 25.00 20.00 15.00 17.30 10.00 14.82 5.00 0.00 Beef Exclosure Beef Meadows Figure 7: Comparison inside and outside exclosure at Beef Meadows site (Fishlake National Forest). Beef Meadows contains an exclosure that has been in place since 1986. Grazing outside the exclosure for the last two years has been permitted for 611 cattle during the month of August. Inside the exclosure, hummocks are, on average less dense (7b), less oblate (7c) and shorter (7d), however due to the small sample size, these findings are not statistically significant. The scatter plot (7a) shows height and width for all hummocks measured at the two sites. The trend of the grazed hummocks is farther from the equal length/width line (dashed line in plot) than the exclosed hummocks. The height graph (7d) has error bars showing one standard deviation above and below the mean. 14
8a) 60 Length vs Width 50 Length (cm) 40 30 20 1:1 L./W ratio Garkane PP King's Pasture 10 0 0 20 40 60 Width (cm) 8b) Hummocks/hectare Hummock Density 12000 10000 10465 8000 6000 4000 4485 2000 0 Garkane PP King's Pasture 8c) 1.40 1.30 1.20 1.10 1.00 Oblateness 1.36 1.20 Garkane PP King's Pasture 8d) Centimeters Hummock Height 30.00 25.00 20.00 15.00 10.00 5.00 0.00 19.21 Garkane PP 17.02 King's Pasture Figure 8: Comparison at Garkane Power Plant and King s Pasture (sites separated by fenceline). Sites are on adjacent parcels of private pasture. King s Pasture has been grazed only by trespass cows for the last ten to fifteen years. Since the construction of a new fence three years ago, there has been no livestock grazing in King s Pasture. Garkane Power Plant grazes at a higher intensity than the Forest Service would typically allow. The trend of the Garkane hummocks is further from the equal length/width line (dashed line in plot) than the King s Pasture hummocks (8a). On the King s Pasture side, hummocks are, on average, less dense (8b), less oblate (8c) and shorter (8d), however due to the small sample size, these findings are not statistically significant. The height graph (8d) has error bars showing one standard deviation above and below the mean. 15
Discussion Push-up, cut-down or both? Hummock formation processes fall into two broad categories, push-up and cut-down. Push-up processes include frost heave, and senescing vegetation. In these, hummocks are built up above the surrounding surface of the ground. Conversely, cut-down processes remove or compact sediment, cutting down the interspace between areas that eventually become hummocks. In many sites, the characterization is difficult, but in at least a few sites surveyed, cut-down processes were clearly at play. Figure 9: Hummocks at Ute Cabin Spring. At the site, the presence of an old pumphouse shows that the hummocks are likely formed by a cut-down process. Erosion has exposed the foundation of the pumpouse, which was originally poured in a form laid at groundlevel. Hummock height is in line with the exposed foundation of the pumphouse which indicates that the ground surface in the area was once at the height of the tops of the hummocks. The interspace has then been cut down from that height. 16
Figure 10: Hummocks at Round Mountain. Hummocks appear to be forming as a slope retreats, a cut-down process. Behind the photographer is a draw about 2 m deep that drains a meadow. Note serpentine shape of many hummocks, shearing on the edges and bare interspace. A band of smaller hummocks with vegetated interspace appears in the upper left of the photo. These may have formed during a previous period of hummock formation or by a different process. 17
Hummock shape At the sites surveyed, hummock oblateness (measured by the ratio of hummock length to hummock width) ranges from 1.16 at Wilcox Flat to 1.94 at Racetrack Reservoir. Hummocks tend to be oblong rather than circular. Schunke (1977) found that hummocks on gentle gradients are often circular with flat tops while steeper slopes display more elongate mounds with low-angled sides. In his study, hummocks most frequently elongated downslope though some extensions occur diagonally across slope or parallel to the contour on gradients of up to 3 (5.2%). In this study, many sites appear to have hummocks elongated across slope, however hummock orientation was not directly measured. At least one site in this survey with a slope over 5%, Round Mountain (slope 9%), has hummocks elongated across or parallel to slope. Hummocks elongate across slope rather than downslope, especially in areas of steeper slope, may be an indicator that cattle trailing along creeks or draws is affecting hummock morphology. Cattle trailing along linear bodies of water is common because it requires less energy than moving up and down slope. Some hummocks have a serpentine shape, with significant sinuosity in addition to being oblate. I could find no literature related to cryogenic or vegetation formed hummocks that mentions this hummock shape. There may be some positive feedback loop occurring and interacting with the trailing of cattle. As cattle follow the same trails, these trails begin to deepen, especially in moist, compactible soils. The trailing removes vegetation and deepens the hummock interspace causing increased channelization of water and decreased overland flow, leading to increased 18
erosion. As the interspace deepens, cows are more likely to walk through those areas in order to minimize their amount of energy expended. It seems reasonable that hoof-shearing on the sides of hummocks could cause the serpentine shapes observed. Figure 11: Serpentine shaped hummock at Webb Hollow. Length is about a meter. The hummock widens toward the ends and thins in the middle with a pronounced bend. Interspace is covered in water and devoid of vegetation. Hummock response to grazing pressure Studies (e.g. Grab 2005, Smith et al. 2012) attribute hummock genesis to a variety of factors such as climate, vegetation community, etc. In order to control for as many factors as possible, hummock sites split by fencelines provide the best indication of how grazing impacts hummock morphology. Unfortunately, only two 19
sites like this were captured in this study, at Beef Meadows and King s Pasture/Garkane Power Plant. The sites at King s Pasture and Garkane Power Plant provide an important look into how different grazing management might alter the degree of hummocking. Both sites are inholdings that lie adjacent Figure 12: Fenceline between King s Pasture and Garkane Power Plant inholdings. King s Pasture (left side of the fence) has significantly less hummocking. to each other on the south side of Boulder Mountain and lie on the east side of a small creek. They lie within the Dixie National Forest. Livestock have grazed at the sites for at least a century. However, King s Pasture has been grazed only by trespass cows for the last 10 to 15 years. Since the construction of a new fence three years ago, there has been no livestock grazing in King s Pasture. Garkane Power Plant grazes at a higher intensity than the Forest Service would typically allow. Hummock density on the Garkane side is much higher than at King s Pasture (10,465 hummocks/hectare vs 4485 hummocks/ hectare). On average, hummocks at Garkane Power Plant are more than 2 cm taller (17.0 cm vs 19.2 cm). A lack of litter cover allowed an easy comparison of the shape, height and density of hummocking at these locations. The comparison between these two adjacent sites 20
suggests that, in this location, grazing exerts some control on hummock morphology and density. Elongate hummocks, common on the Garkane side, are longer parallel to stream direction and perpendicular to slope. This is counter to the findings of Shunke (1977), who observed that earth hummocks are typically elongate downslope. Elongation parallel to stream direction may be due to trailing of cattle along riparian corridors. Similar results were found at Beef Meadows (see Figure 7). Hummocks are taller, denser and more oblate in the active grazing area outside the exclosure. These findings provide intriguing avenues for future research. More paired sites such as these should be surveyed to strengthen these observations. Exclosures are present at Grass Lake and Danish Meadows, though they were not surveyed in the study due to time and resource constraints. Cautions regarding exclosures and fencelines While helpful in comparing hummocked sites with different grazing histories, a few complicating factors must be noted. First, exclosed areas in almost all cases have more vegetative cover because the grazing pressure has been significantly reduced. When visually estimating the degree of hummocking in an exclosure, this cover creates a more uniform appearance and hides underlying hummocks. This can create the visual impression that there is less hummocking at the site, which may or may not actually be the case. It is necessary to physically examine the site before drawing conclusions about the extent of hummocking. All exclosures exhibit significantly more litter cover because the vegetation is not being grazed. This cover 21
tends to fill in interspace, creating the impression that the hummocks are smaller. It also introduces difficulty in measuring the hummocks. In order to measure height, width and length its necessary to remove a significant amount of litter from on and around the hummock. It may also be true, though, that the litter accumulating in the interspace is decomposing and building soil, decreasing hummock height in actuality as well. Regarding fencelines, cattle tend to trail along fencelines, especially when better forage is present on the other side of the fence. Therefore, cattle impacts are often most severe directly along fencelines. These areas, while visually arresting, should not be interpreted as representative of entire sites. Large, flat hummocks at Beef Meadows and Stink Flat While Beef Meadows and Stink Flat have conventionally sized hummocks, both also have wide, flat hummock features that may be forming from a different process. These features near the edges of large hummock fields are more than 2 m long in places; the height of the features is close to that of the conventional hummocks which concentrate in the centers of the sites. Grab (1998) found hummock size Figure 13: Large hummocks, Stink Flat. 22
within sites to vary with soil moisture, with hummocks near the dry periphery being smaller, more widely spaced and less developed. While this is the case at some sites surveyed (e.g. Round Mountain), the opposite is true (at least in terms of size) at the Beef Meadows and Stink Flat sites. Large pockets of rocks are exposed within some of these large hummocks (Figure 14). What produces these collections of exposed rock? Perhaps the ground surface was higher and has eroded away, leaving the Figure 14: Exposed rocks at site margin, Stink Flat larger clasts that could not be carried away by wind or water. It may be possible that frost push and pull has exposed these clasts by cryoexpulsion. If this is the case, rocks that have been pulled near the surface but have not yet been exposed to the surface may form these larger hummocks. No cross-sections were performed on any of these larger hummocks, so it is unknown whether they contain large clasts. These large hummocks are found near other types so a similar process may be controlling both. 23
Conclusion This initial survey of Utah s wetlands cannot prove or disprove grazing as a factor leading to hummock formation. No relationship was found between elevation and the degree of hummocking within sites which would have suggested a cryogenic mechanism of formation. This survey does provide intriguing observations regarding the role of ungulate activity in exacerbating hummocks. Direct comparisons of hummocks at Garkane Power Plant/King s Pasture and Beef Meadows reveal that hummocks are Site Height (cm) Oblateness (L/W) Beef 17.3 1.67 10465 Meadows Beef 14.8 1.36 7475 Exclosure Garkane PP 19.2 1.36 9717 Density (hummocks/hectare) King s Pasture 17.0 1.20 7475 Figure 15: Summary table of Garkane Power Plant/King s Pasture data. more tall, more oblate and that the hummock fields contain more hummocks per unit area at the sites with more grazing. These results, while not statistically significant, open avenues for further research in this area. Several reccommendations can be drawn for forest service managers in southern Utah from this research. 1. Larger areas ungrazed by cattle are needed on the forests to serve as reference areas to better understand the impact grazing has for various types of ecosystems. 2. A formal definition for what constitutes a hummock should be developed in order to facilitate communications between the scientific community and the 24
Forest Service. A distinction should be made between hummocks formed by depositional processes (push-up) and erosional processes (cut-down) 3. Hummocking should be used in conjunction with other indicators to assess riparian health. Hummocks can channelize water in riparian areas, lead to less productive species and allow higher utilization of wetland species by ungulates by decreasing the distance between the plants and the ungulate s mouth. 4. Priority should be given to hummocked areas with hummocks of elongated or serpentine shape. These hummocks are less likely to be caused by natural processes. Future research should focus on the morphology of both individual hummocks and hummock fields. Measurements should be taken on more individual hummocks within a field to provide statistically valid comparisons between sites. Measuring the orientation of the long axis of hummocks would allow comparison with the orienation of features like streams or the aspect of the site. More directly comparable sites should be surveyed though the prevalence of grazing throughout the Fishlake, Dixie and Manti-La Sal National Forests complicates finding such areas. Large areas should be set aside from cattle grazing to serve as reference areas in order to make clearer distinctions between areas under a livestock regime and those not. Until such a time, exclosures or other areas where grazing style is significantly different within a small area are likely a researcher s best options for studying hummock genesis. 25
Acknowledgments Many, many people deserve thanks for their help on my thesis. First to my supervisor, mentor and friend, Mary O Brien for handing me this project in the first place. You always push me to do more than I ever thought I could. To her husband, O B, for statistical and mental health support. Thank you to my thesis adviser, Bob Carson, for taking hours and hours to mull over these bumps in the ground with me. Thank you to all of the scientists out there looking at hummocks in the West, and to Dave Weixelman, Paul Meiman and David Cooper especially, my deep appreciation for your time and for your invaluable insight. My gratitude to Bob Beschta for bringing in the ecologist s point of view. Special thanks to the federal land managers and scientists who worked with me and consulted on this project, Brooke Shakespeare, Kurt Robins, Lisa Bryant. Thank you to the Whitman College Environmental Studies Department and the Grand Canyon Trust for funding to complete this research. And finally, to my beloved field assistants: Bryn Gerson, Emmi Colunga, Emma Woodworth and Linnaea Weld. Thanks for putting up with the senior intern and for all your hours spent crawling through muddy hummock fields (or mapping them). I couldn t have done it without you. 26
References Cited Booth, D.T., Cox, S.E., Likins J.C. (2014) Fenceline contrasts: grazing increases wetland surface roughness. Wetlands Ecological Management (23) 2:183-194. Chimber, RA, Cooper, DJ. (2003) Carbon Dynamics of Pristine and hydrologically modified fens in the southern Rockies. Canadian Journal of Botany, 81:477-491. Corning RV (2002) Diminished sweetwater river flows from the high cold desert region of Wyoming. A whitepaper included in Part III of the 2002 Green Mountain Common Allotment Evaluation, Lander Field Office, Bureau of Land Management. Girard M, Wheeler DL, Mills SB (1997) Classification of riparian communities on the Bighorn National Forest. USDA Forest Service Rocky Mountain Region R2-RR-97-0. Grab, Stefan. (1998) Non-sorted patterned ground in the High Drakensberg, Southern Africa: Some New Data. The Geographical Journal (164) 1:19-31. Grab, Stefan. (2005) Aspects of the geomorphology, genesis and environmental significance of earth hummocks (thúfur, pounus): miniature cryogenic mounds. Progress in Physical Geography, 29 (2):139-155. Janovsky-Jones, Mabel. (1999) Conservation strategy for wetlands in east-central Idaho. Idaho Department of Fish and Game. 600 South Walnut, P.O. Box 25, Boise, ID 83707. Kovalchik, B.L., Elmore, W. (1991) Effects of cattle grazing systems on willowdominated plant associations in central Oregon. Presented at Symoposium on ecology and management of riparian shrub communities. Sun Valley, ID, May 29-31, 1991. Lessica, P., Kannowski, P.B. (1998) Ants create hummocks and alter structure and vegetation of a Montana fen. American Midland Naturalist, 139(1):58-68. Magnusson B, Elmarsdottir A, Barkarson BH (1998) Horse ranges a method to assess range condition. Agricultural Research Institute, Keldnaholt, 112 Reykjavik, Iceland. http://www.rala.is/umhvd/hhagar/edefault.htm. Accessed March 1, 2015. Smith, M.L., Meiman P.J., Brummer, J.E. (2012) Characteristics of hummocked and non-hummocked Colorado riparian areas and wetlands. Wetlands Ecological Management, 20:409-418. Schwinning, S. Belnap, J., Bowling, D.R., Ehleringer. (2008) Sensitivity of the Colorado Plateau to change: climate, ecosystems, and society. Ecology and Society (13) 2, Article 28 (online). 27
Snee, J.L., Carson, R.J. (year) Terracettes: animal, vegetable, or mineral? Thesis, Whitman College Department of Geology. Walla Walla, WA. Streeter, R, Andrew, AJ. (2013) Anticipating land surface change. Proceedings of the National Academy of Sciences (110), 15:5579-5784. Toy, T.J., Hadley, R.F. (1987) Geomorphology and reclamation of disturbed lands. Academic Press, Orlando Florida. Ch. 6 Lands Disturbed by Grazing (pp.152-162). Trimble, S.W., Mendel, A.C. (1995) The cow as a geomorphic agent A critical review. Geomorphology (13), 233-253. Van Vliet-Lanoë B., Seppälä M. (2002) Stratigraphy, age and formation of peaty earth hummocks (pounus), Finnish Lapland. Holocene 12:187-199. Verbeek NAM, Boasson R (1984) Local alteration of alpine calcicolous vegetation by birds: do the birds create hummocks? Arctic Alpine Research 16:337 341. Washburn, A.L. (1956) Classification of patterned ground and review of suggested origins. Bulletin of the Geological Society of America 67:823-865. Weixelman, D.A., Cooper, D.J. (2009)Assessing Proper Functioning Condition for Fen Areas in the Sierra Nevada and Southern Cascade Ranges in California. United States Forest Service. 28
Appendix I: Standard Operating Procedure: Riparian/Wet Meadow Hummock Survey A. Definitions 1. Hummock- For the purposes of this survey, a hummock was considered to be a knob-like feature on the ground at least three inches tall with relief on all sides. 2. Interspace- Area between hummocks. 3. Site- A hummocked area at least 15 yards long and 15 yards wide. Hummocks must be no more than 15 yards apart to be considered at part of the same site. 4. Edge- determined either where hummocking stops, hummock features become less than 3 inches tall, or spacing between hummocks becomes greater than 15 yards. a. Gradational- Hummocks become smaller than 3 tall. b. Headcut- Hummocking ceases at a bare slope c. Running water- Hummocking ceases at a feature of running water (e.g. a stream) d. Distinct- Hummocking ceases in a way not described by the above. 5. Canopy- The top vegetation or litter to hit the point transect pointer a. Grass- Member of the graminoid family b. Grass-like- Sedges, rushes, bulrushes etc. c. Forb- flowering, vegetative plant d. Shrub- Woody plant with multiple stems emerging near the base e. Tree- Woody plant with single main stem/trunk 6. Ground- Ground type where the pointer touches the ground a. Vegetation- Live plant b. Litter- Dead plant or other detritus (e.g. scat) c. Water- Ground is wet enough to reflect light d. Bare- Soil with none of the above types. B. Site Characterization 1. Site Name: Use the name of area (e.g. Bown s Lake) or a nearby landmark (Pond near Nizhoni Campground) 2. Date 3. Location: Take GPS point near center of site, use UTM NAD 83 4. Slope: Find highest edge of site and lowest edge of site. Use a clinometer to take the slope between these two points and record as percent slope. It is helpful to use a range pole to gauge where to line the clinometer up. Find the height of your eye on the range pole when it is right next to you and sight the same place on the range pole when it is across the site. 29
5. Aspect: Use the same two points used for slope. Use a Brunton compass to find the bearing in degrees from the high point to the low point. A non- Brunton compass can be used with less accuracy. 6. Allotment and Pasture: Can be found from maps provided by the US Forest Service website 7. Site length- Find using transect tape to connect two furthest edges to each other. Leave transect tapes, they will be used for the point transect at the site 8. Site width- Use range finder to find distance at widest axis perpendicular to the site length. a. Note on length and width: If necessary, GPS points can be taken at the edges of the site and distance determined by a program like Google Earth or ArcGIS when out of the field 9. Surveyors: Use first initial and last name 10. Scat- Record whether cow, deer or elk scat is observed. If more than 3 of a particular type is observed at a site mark abundant. C. Point Transect 1. Use a random number generator or random number table to find three random numbers within the long axis length. Record these numbers 2. Use a transect tape to measure the width of the site perpendicular to the long axis at those points. The distance should be measured to the end of the last 3 hummock or to the base of a headcut if one is present. Record these three distances. a. If no edge can be determined along the perpendicular, choose a different random location along the long axis. 3. Add the three perpendicular distances to find the total transect length. Record. Divide the total transect length by 100 to find the transect interval (round to the nearest hundredth of a foot) 4. For very large sites, an alternative sampling procedure was used. From a point near the center of the site, a random direction and number of steps was selected and used to find the transect start. From the start, a random direction was chosen for the transect. If an edge was encountered, the researcher turned around and paced out the remaining steps back towards the center point. This method was employed at Beef Meadows, Stink Flat and Danish Meadows. 5. Use a random number between 0 and the length of the transect interval to find the distance of the starting point (Point 1). 6. Record the distance of each point on the transect by adding the transect interval to the previous point distance. There should be 100 points within the total transect length. 7. Set up the transect tape at the furthest downstream transect location. 8. Begin reading the transect- Place a narrow pointer on the right side of the transect tape perpendicular to the ground at the point location. Find the vegetation that hits highest on the pointer. Determine whether the 30
vegetation is a grass, a grass-like plant, forb, shrub or tree (refer to definitions). If the vegetation is grass or grass-like, record whether it is rhizomatous or caespitose. If the vegetation is dead, record litter. If no vegetation is hit, record x for no hit. 9. Read where the pointer hits the ground as bare, litter, vegetation, water or rock. If the ground is vegetation, make a note of the type. 10. Read whether the pointer lies on a hummock or in interspace. The hummock begins where the ground begins to rise above the level of the interspace. 11. Take a note of any interesting features on or around the point. This could include plant species or notes about a hummock hit etc. 12. Repeat steps 7-10 for all 100 points. a. IMPORTANT: When moving the transect tape between locations, make sure to start the tape on the same side each time. Start the tape at the total length of the previous transect or two transects. D. Hummock Plots 1. Hummock plots are conducted along the transect at points 30, 48, 71 and 91 (randomly selected). 2. To construct a 6 x 6 plot, place the range pole along the transect tape so that the center lines up with the distance of the plot point, with three feet extending in each direction. Mark the ends of the range pole along the transect tape with colored flags. These are the first two corners of the plot. Pick up the range pole and place one end at one of the flags, with the pole laying perpendicular and to the left of the transect tape, extending. Have one surveyor hold the range pole and another watch the intersection of range pole and transect tape to find where the range pole is perpendicular. Place a flag at the other end of the range pole for the third corner of the plot. Repeat this process on the other side for the fourth corner. 3. Place a white flag on each hummock that falls at least half inside the plot. Record the number of hummocks in the plot. 4. Find the hummock closest to each corner that lies off of the transect. Measure the long axis, width perpendicular to the long axis and height of each hummock. Height is measured from the interspace to the apex of the hummock. If there is only one hummock in the plot, record the length, width and height of that hummock. 5. Take picture of plot 31
Transect line Hummock not included in plot Counted but not measured Measured hummocks 6 Figure 16: Diagram of Hummock Plot E. Soil Samples 1. At each plot location (Points 30, 48, 71, 91) and additionally at point 73 (randomly selected), take a soil sample to create an aggregate soil sample for the site. 2. Use a cylindrical soil sampler to take a soil core at the point, directly to the left of the transect tape. Try to make the core 6 in length and at least ¾ in diameter. This may be difficult in wet or poorly consolidated soils or soils with dense organic matter (like at sod mat) on the surface. Place the sample in a plastic bag and record the site, date and the depth of the sample. 3. Samples from different points should all be placed in the same bag to create an aggregate sample. 32
4. Seal samples well in the field and place in a refrigerator until textural analysis equipment becomes available. Plot procedure adapted from: Smith et. al. 2012. Characteristics of hummocked and non-hummocked riparian areas and wetlands. Wetlands Ecology Management 20:409-418 33
Appendix II: Aggregate Site Data 34
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